Voltage regulating circuit arrangements



United States Patent O 3,013,197 VOLTAGE REGULATING CIRCUIT ARRANGEMENTS Anthony Norman Heightman and Walter Thomas Underhill, Great Baddow, England, assignors to Marconis Wireless Telegraph Company Limited, London, England, a British company Filed Dec. 19, 1958, Ser. No. 781,571 Claims priority, application Great Britain Mar. 7, 1958 3 Claims. (Cl. S20-1) This invention is for improvements in or modifications of the invention contained in the specification of application Serial No. 706,122, relating to voltage regulating circuit arrangements.

The present invention, like the parent invention, makes use of devices of the saturable transductor reactor type. This type of device, as is well known, is a reactance device having a core whose hysteresis loop (B-H magnetisation curve is of approximately rectangular shape. The impedance presented by a winding on the core of a device of this type is very low when the core is saturated and vvery highwhen it lis not. To quote a typical practical casre,ithe current` passed by the winding of such `a device under given conditions of applied voltage and frequency mayfall from a figure of the order` of 8. amperes when the core is saturated to a figure of the order of ma. when the core is not. Such a device therefore approximates to a switch which can .be controlled by changing the condition of the core from the saturated to the non-saturated condition or vice-versa, although, of course, the switch has no true open circuit position The parent specification described a number of voltage regulating circuit arrangements wherein voltage from a source of A C. voltage is rectified and the rectified voltage employed to charge a reservoir condenser through a charging circuit which includes a winding of a saturable transductor reactor having a core with a near-rectangular hysteresis loop, the magnetisation of said core being ladditionally controlled in accordance with the output voltage-which is the voltage across said condenser-by means including the anode-cathode space of a valve which is controlled by said output voltage. In the particular arrangements described in the parent specification the controll by the valve is obtained by connecting the anodecathode space thereof in series with the aforesaid winding in a discharging circuit for said condenser. Also the rectification is effected by means of a bridge rectifier. One feature of the present invention provides improved or modified circuits in which the valve is employed to effect control of the magnetisation of the core in dependence upon output voltage by controlling the current through an additional winding o-n the core. As will be seen later this may have advantages over the circuits described in the parent specification. Another feature of the present invention provides a voltage doubling rectifier in place of the bridge rectifier of the circuits described in the parent specification. Among the advantages possessed by this is that the number of rectifying diodes required is reduced and, in the case of apparatus which may have to withstand a wide range of ambient temperature e.g. in the case of apparatus for tropical use-this will usually mean a substantial economy, for rectifiers suitable for tropical use are expensive.

According to a -feature of this invention a voltage regulating circuit arrangement comprises means for rectifying voltage from a source of applied A.C. voltage, at least one reservoir condenser, a charging circuit for charging said condenser from the rectified voltage, said circuit including a winding of a saturable transductor reactor having a core with a near-rectangular hysteresis loop, a circuit including said winding and a resistance in the first feature of this invention.

3,013,197 Patented Dec. 12, 1961 ICC series with one another across said condenser, means for taking voltage from said condenser for output, and additional means controlled in dependence upon the output voltage for controlling the magnetisation of said core, said additional means comprising a further winding on said core and a valve which is controlled in dependence upon said output voltage and has its anode-cathode space connected to control the current through said further winding.

According to another feature of this invention a volt age regulating circuit arrangement comprises a saturable transductor reactor having a core with a near-rectangular hysteresis loop and at least two windings on said core; ak

first reservoir condenser; a first circuit including a source of A.C. potential, a first rectifier, and one of said windings for charging said first condenser; a second reservoir condenser; a second circuit including said source of A.C. potential, a second rectifier, and the second of said windings for charging said second condenser, the two rectifiers being connected in opposite senses whereby one passes current in alternate half-waves of the A.C` voltage from said source and the other passes current in the remaining half-waves of said A C. voltage; means for taking output from across the two reservoir condensers; and additional means, including the anode-cathode space of a valve controlled in dependence upon said output voltage, for controlling the magnetisation of said core. As in the case of circuits as described in the parent specification the rectifiers will tend to pass a certain amount of current in the reverse direction and this of course tends to limit the range of control by the valve 6. This defect may be reduced or eliminated by passing the load current through a few turns wound on the reactor in such sense as the oppose the magnetisation due to the rectifier reverse current. If an extra winding constituted by these few turns is provided, it will, of course, introduce positive feedback and accordingly, if such an extra winding is provided, care must be taken that it is not such as to cause instability.

Both features of this invention may be used together. In one embodiment in which this is done a voltage regulating circuit arrangement comprises a saturable transductor reactor having a core with a near-rectangular hysteresis loop and at least three windings on said core; a first circuit including a source of A.C. potential, a rst rectifier, one of said windings and a first reservoir condenser for charging said first condenser; a second circuit including said source of A C. potential, a second rectifier, the second of said windings and a second reservoir condenser for charging the said second condenser, the two rectifiers being connected in opposite senses whereby one passes current in alternate half-waves of the A.C. voltage from said source and the other passes current in the remaining half-waves of said A C. voltage; means for taking output from across the two reservoir condensers; a circuit including one of said windings and a resistance in series with one another across both said condensers; a further winding on said core and a valve controlled in dependence upon said output voltage and having its anode-cathode space connected to control the current through said further winding.

The invention is illustrated in and further explained in connection with the accompanying drawings in which FIGURES 1, 2, 4, 5 and 6 are diagrams of tive embodiments, FIGURE 3 is an explanatory graphical figure, FIGURE 7 depicts graphical representations of voltage, current and magnetic flux in embodiments of this invention, and FIGURE 8 is a B-H diagram of the saturable reactor employed in this invention.

Referring to FIGURE 1, this shows an embodiment of It will be seen that the accompanying FIGURE l is in many respects similar to FIGURE 1 of the drawings of the provisional specification of the parent case. A.C. input voltage is applied at terminal 1 through a transformer 2 to the ends of one diagonal of a bridge rectifier comprising four rectifiers 3. One end or the remaining diagonal is connected to one of the two output terminals 8 through a winding 4 on the core of `a saturable transductor' reactor, the said core having a near-rectangular hysteresis loop. Between the terminals S is a reservoir condenser 5 and also a potentiometer resistance 73, a tap 72 of which supplies voltage to a DC. amplifier 71 which amplies the said voltage for application to the control grid of a valve 61. This valve is in series with a second winding 41 across the output terminals S. A resistance 90 is connected as shown across the ends of the output diagonal of the rectifier bridge. In FIGURE l, as in FIGURES 2, 4, 5 and 6, the letters S and F are used to indicate start and nish of the windings to which they are applied. It will be seen therefore that the windings 4 and 41 oppose one another magnetically.

ne arrangement of the accompanying FIGURE 1 differs from that of FIGURE 1 of the parent specification in the way in which output voltage control of the magnetisation of the core of the reactor is obtained. In the accompanying FIGURE l the resistance 90 draws what may be termed bias current for the core through the Winding 4. The blas current is derived from the reservoir condenser and passes from this condenser through the winding 4 and resistance 9d to the other side of the condenser. The rectnier current liow through the winding 4 in the direction of the upper output terminal 8 (in FIGURE 1) is such as to produce saturation of the core in one direction while the bias current flow in the opposite direction is sucn las to produce not far short of core saturation in the opposite direction. The valve 61 produces, by means of the coil 41, the required control of core magnetisation. The magnetisation caused by the valve current through coil 4I. opposes that due to the current flow through resistance 91B and coil 4. The valve current, varying under the varying grid potential, produces a net magnetisation such that the output voltage is maintained at the required valve.

An operational difference between the circuit of the accompanying FIGURE 1 and that of FIGURE 1 of the parent specification is that the operating control effect of the valve 6I is reversed with respect to that obtained with the valve 6 of FIGURE 1 of the parent specification. This may in some cases be an advantage for it means that if pre-amplification of the voltage to be applied to the grid of the control valve is required a single stage amplifier will sufiice for such pre-amplification whereas, in the case of FIGURE 1 of the parent specification, a two valve amplifier would have to be provided.

FIGURE 2 shows an embodiment of the second feature of this invention. Here, in place of the rectifier bridge with its four rectifiers, only two rectifiers, namely the rectifiers 31 and 32, are employed. In place also of a single reservoir condenser there are two similar reservoir condensers 51 and 52. The transformer secondary is connected across a circuit consisting of a rectifier 31, a winding 42 on the reactor and one condenser 51 and it is also connected across a circuit consisting of the rectifier 32, a second winding 43 on the reactor core and the second condenser 52. The two windings 42 and 43 are in magnetic opposition as indicated by the letters S and F. The control valve, here numbered 62, has its anodecathode space connected between the junction point of the elements 31 and 42 and the output terminal side of the condenser 52, and voltage proportional to that produced between the output terminals is applied at terminal 7 to the control grid of the said Valve 62. The voltage at the terminal 7 may be obtained in arly Convenient Way, eg. by means of a potentiometer and D.C. amplifier as in the accompanying FIGURE 1. The operation 0f the rectifier circuit included in FIGURE 2 is illustrated graphically from FIGURE 3, the upper line of which represents current (plotted against time on the horizontal axis) through the rectifier 31 and the lower line of which similarly represents current through the rectifier 32. The time period C is the time taken by one cycle of the alternating current supply. It will be seen that, as one winding (42 or 43) is included in the circuit of each halfwave rectifier (31 or 32), and as the half-wave current pulses occur alternately (see FIGURE 3) the effect as regards the core of the Atwo windings 42 and 43, is the same as if full-wave bridge rectification with the halfwave pulses occurring in a single winding (as inthe parent specification) were employed.

FIGURE 4 shows a minor modification of the circuit of FIGURE 2. The modification consists in the fact that instead of connecting the anode of the valve 62 to the junction point of the elements 31 and 42, there is provided an additional fine wire winding 44, and the anode of the valve 62 is connected to the end of this extra winding. This results in a higher voltage (as compared to the circuit of FIGURE 2) being applied to the valve, the advantage cf the increased number of turns in the valve circuit being that, for a given number of ampere turns, less current is required from the valve and a smaller valve can be used. The extent of reduction of valve current achievable in this way is limited by the effect that the back of the additional winding deprives the valve of anode voltage.

FIGURE 5 shows a further minor modification of the circuit of FIGURE 2. The modification consists in providing a few extra turns 45 wound over the coil 42 and included in series in the output circuit. These extra turns are for the purpose of compensating for rectifier reverse current.

FIGURE 6 shows an embodiment incorporating both features of this invention. Its nature will, it is thought, be fairly self evident from the figure itself, since like references are used for like parts throughout the drawings. As will be apparent, rectification is effected by a voltage doubling rectifier arrangement incorporating the rectifiers 31 and 32 as in FIGURE 2, while output voltage control of the magnetisation of the reactor core is effected by a winding 41 on the core in manner very similar to that employed in the circuit of the accompanying FIGURE 1.

A cycle of operation is described with the aid of the voltage, current, and flux-waveforms of FIG. 7 and the B--H diagram of FIG. 8. For the sake of clarity, some details of the waveforms observed in practice have been omitted. The numbered points in the two figures represent the same instants in time. As full-wave rectification is employed, the cycle of operation repeats every halfcycle of the A.C. input wave.

At the start of a half-cycle, under steady-state conditions, the A.C. input wave passes through zero and increases positively. At the instant indicated at (1) the input reaches a voltage equal to that at the reservoir capacitor, and the appropriate pair of rectifier arms of the bridge begins to conduct, applying the input voltage to the transductor and reservoir. At this time the transductor is not saturated, as shown by the B-H diagram, so that only the small magnetizing current of the transductor flows into the reservoir, and negligible charge is acquired. In order to support the impressed voltage the transductor core fiux must change, until at (2) saturation is reached.

With the core saturated, and the transducer impedance very small, full rectifier conduction occurs, the core being driven further into saturation. The reservoir charge increases until at (3) the reservoir voltage is equal to the instantaneous input voltage, and rectifier conduction then ceases as the input Voltage, proceeding in its cycle, falls below that at the reservoir. As the magnetizing force falls to zero the core fiux returns to the remanent point (3).

With the rectifier branch non-conducting the path containing the transductor, control valve and reservoir becomes effective. It will be seen that the reservoir voltage is applied to the transductor via the valve, and that the polarity of this voltage at the transductor terminals is opposite to that applied from the rectifier bridge when conducting. The valve grid has some steady potential enabling yit to conduct. Thus, from the instant (3) the core flux begins to fall from the remanent value. The fall continues until rectifier conduction recommences at (1) in the succeeding half-cycle; the valve current then being drawn from the rectifier.

Itis convenient to assume that the fiux change occurring dur-ing the control period depends simply on the valve current. Thus, if the valve current is zero the core remains at the positive remanentv tlux level. If lthe valve current is at a maximum the core will reach negative saturation.

The charge acquired by the reservoir in each half-cycle, and hence the mean output voltage, depends on the time for which full-conduction of the rectiiiers can occur. If the transductor core has remained at saturation during the control period, then when the instantaneous A.C. input voltage equals the reservoir voltage, full-conduction occurs at once. Under this condition, the rectifier circuit behaves substantially as it would without the transductor, and a maximum relative output voltage is obtained. An additional voltage drop is caused by the Winding resistance of the transductor, but in a suitable design this resistance will be only about 1% of the load resistance, so that the drop is quite small. With suitable core structure the saturated reactance will have a negligible effect on the mean output voltage.

If, on the other hand, the core is at negative saturation at the instant that the rectiiier is able to conduct, the transductor Will prevent full-conduction While the core moves toward positive saturation under the influence of the applied E.M.F. The charge then received by the reservoir in each half-cycle will have its minimum value, resulting in a minimum relative mean output voltage.

The D.C. output for a given A.C. input is thus a function of the control valve current and hence of its grid potential. The output voltage can therefore be held constant while the A.C. input and load current vary, by suitable variations in grid potential.

We claim: v

1A. A voltage regulating circuit arrangement comprising a saturable transductor reactor having a core with a nearrectangular hysteresis loop and a rst, a second and a third winding on said core; first and second reservoir condensers; a first circuit for charging said first condenser including a source of A.C. potential, a first rectifier, and one of said windings, a second circuit for charging said second reservoir condenser including said source of A.C. potential, a second rectifier, and the second of said windings, the two rectiers being connected in opposite senses whereby one passes current in alternate half-waves lof the A.C. voltage from said source and the other passes current in the remaining half-waves of said A.C. voltage; means for taking output from across the two reservoir condensers; a third circuit including said one of said windings and a resistance in series with one another across both said condensers; and a valve controlled in dependence upon said output voltage and having its anode-cathode space connected to control the current through said third winding.

2. A voltage regulating circuit arrangement comprising a saturable transductor reactor having a core with a nearrectangular hysteresis loop and at least two windings in magnetic opposition on Said core; a first reservoir condenser connected to one of said windings; a first circuit including a source of A.C. potential, a first rectifier and one of said windings for charging said first condenser; a second reservoir condenser, said condenser being connected to the other of said windings; a second circuit including said source of A.C. potential, a second rectifier, and the second of said windings for charging said second condenser, the two rectifiers being connected in opposite senses whereby one passes current in alternate half-waves of the A.C. voltage from said source and the other passes current in the remaining half-waves of said A.C. voltage; means for taking output from across ythe two reservoir condensers; a thermionic valve having its anode connected to the junction between said lirst rectiiier and one of said windings, the cathode of said valve being connected to the end of said other winding joined to the second reservoir condenser and one output lead, and means for applying to the control grid of said valve voltage proportional to the output voltage for controlling the magnetization of said core.

3. An arrangement as claimed in claim 2 comprising an addi-tional winding arranged to produce magnetization of the sense to oppose the magnetization due to the rectifier reverse current on said reactor, means for passing the load current through said additional winding whereby reverse limitation of control by the rectifier current is reduced.

References Cited in the file of this patent UNITED STATES PATENTS 

